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Aortic stenosis (AS) is narrowing of the aortic valve obstructing blood flow from the left ventricle to the ascending aorta during systole. Causes include a congenital bicuspid valve, idiopathic degenerative sclerosis with calcification, and rheumatic fever. Progressive untreated AS ultimately results in one or more of the classic triad of syncope, angina, and exertional dyspnea; heart failure and arrhythmias may develop. A carotid pulse with small amplitude and delayed upstroke and a crescendo-decrescendo ejection murmur are characteristic. Diagnosis is by physical examination and echocardiography. Asymptomatic AS often requires no treatment. For progressive severe or symptomatic AS in children, balloon valvotomy is used; adults require valve replacement.
Etiology
Aortic sclerosis, a degenerative aortic valve disease with thickening of aortic valve structures by fibrosis and calcification initially without causing significant obstruction, is the most common cause of AS in elderly patients. Over years, aortic sclerosis progresses to stenosis in as many as 15% of patients. Aortic sclerosis resembles atherosclerosis, with deposition of lipoproteins, active inflammation, and calcification of the valves; risk factors are similar (see Arteriosclerosis: Risk Factors).
The most common cause of AS in patients < 70 yr is a congenital bicuspid aortic valve. Congenital AS occurs in 3 to 5/1000 live births and affects more males.
In developing countries, rheumatic fever is the most common cause in all age groups. Supravalvular AS caused by a discrete, congenital membrane or hypoplastic constriction just above the sinuses of Valsalva is uncommon. A sporadic form of supravalvular AS is associated with a characteristic facies (high and broad forehead, hypertelorism, strabismus, upturned nose, long philtrum, wide mouth, dental abnormalities, puffy cheeks, micrognathia, low-set ears). When associated with idiopathic hypercalcemia of infancy, this form is known as Williams syndrome. Subvalvular AS caused by a congenital membrane or fibrous ring just beneath the aortic valve is uncommon.
Pathophysiology
Aortic regurgitation may accompany AS, and about 60% of patients > 60 yr with significant AS also have mitral annular calcification, which may lead to significant mitral regurgitation.
The left ventricle (LV) gradually hypertrophies in response to AS. Significant LV hypertrophy causes diastolic dysfunction and, with progression, may lead to decreased contractility, ischemia, or fibrosis, any of which may cause systolic dysfunction and heart failure (HF). LV chamber enlargement is a late finding unless there is coexisting MI. Patients with AS have a higher incidence of GI bleeding (called Heyde's syndrome) because the high shear stress of stenotic valves makes multimeric von Willebrand's factor more susceptible to cleavage by a plasma metalloprotease and may increase platelet clearance. GI bleeding may also be due to angiodysplasia.
Symptoms and Signs
Congenital AS is usually asymptomatic until at least age 10 or 20 yr, when symptoms may begin to develop insidiously. In all forms, progressive untreated AS ultimately results in exertional syncope, angina, and dyspnea (SAD triad). Other symptoms and signs may include those of HF and arrhythmias, including ventricular fibrillation leading to sudden death.
Exertional syncope occurs because cardiac output cannot increase enough to meet the demands of physical activity. Nonexertional syncope may result from altered baroreceptor responses or ventricular tachycardia. Exertional angina pectoris affects about two thirds of patients; about half have significant coronary artery atherosclerosis, and half have normal coronary arteries but have ischemia induced by LV hypertrophy, altered coronary flow dynamics, or both.
There are no visible signs of AS. Palpable signs include carotid and peripheral pulses that are reduced in amplitude and slow rising (pulsus parvus, mollus et tardus) and an apical impulse that is sustained (thrusts with the 1st heart sound [S1] and relaxes with the 2nd heart sound [S2]) because of LV hypertrophy. The LV impulse may become displaced when systolic dysfunction develops. A palpable 4th heart sound (S4), felt best at the apex, and a systolic thrill, corresponding with the murmur of AS and felt best at the left upper sternal border, are occasionally present in severe cases. Systolic BP may be high with mild or moderate AS and falls as AS becomes more severe.
On auscultation, S1 is normal and S2 is single because aortic valve closing is delayed and merges with the pulmonic (P2) component of S2. The aortic component may also be soft. Paradoxical splitting of S2 may be heard. An S4 may be audible. An ejection click may also be audible early after S1 in patients with congenital bicuspid AS when valve leaflets are stiff but not completely immobile. The click does not change with dynamic maneuvers.
The hallmark finding is a crescendo-decrescendo ejection murmur, heard best with the diaphragm of the stethoscope at the right and left upper sternal border when a patient who is sitting upright leans forward. The murmur typically radiates to the right clavicle and both carotid arteries (left often louder than right) and has a harsh or grating quality. But in elderly patients, vibration of the unfused cusps of calcified aortic valve leaflets may transmit a louder, more high-pitched, “cooing” or musical sound to the cardiac apex, with softening or absence of the murmur parasternally (Gallavardin's phenomenon), thereby mimicking mitral regurgitation. The murmur is soft when stenosis is less severe, grows louder as stenosis progresses, and becomes longer and peaks in volume later in systole (ie, crescendo phase becomes longer and decrescendo phase becomes shorter) as stenosis becomes more severe. As LV contractility decreases in critical AS, the murmur becomes softer and shorter. The intensity of the murmur may therefore be misleading in these circumstances.
The murmur of AS typically increases with maneuvers that increase LV volume and contractility (eg, leg-raising, squatting, Valsalva release, after a ventricular premature beat) and decreases with maneuvers that decrease LV volume (Valsalva maneuver) or increase afterload (isometric handgrip). These dynamic maneuvers have the opposite effect on the murmur of hypertrophic cardiomyopathy, which can otherwise resemble that of AS. The murmur of mitral regurgitation due to prolapse of the posterior leaflet may also mimic AS.
Diagnosis
Diagnosis is suspected clinically and confirmed by echocardiography. Two-dimensional transthoracic echocardiography is used to identify a stenotic aortic valve and possible causes, to quantify LV hypertrophy and degree of diastolic or systolic dysfunction, and to detect coexisting valvular heart disorders (aortic regurgitation, mitral valve disorders) and complications (eg, endocarditis). Doppler echocardiography is used to quantify degree of stenosis by measuring aortic valve area, jet velocity, and transvalvular systolic pressure gradient.
A valve area of 0.5 to 1.0 cm2 or a mean gradient > 45 to 50 mm Hg represents severe stenosis. The gradient may be overestimated in aortic regurgitation and underestimated in LV systolic dysfunction. The rate of progression of AS from mild to severe is quite variable and does not necessarily proceed in a linear fashion.
Cardiac catheterization is necessary to determine whether coronary artery disease (CAD) is the cause of angina and, occasionally, to resolve differences between clinical and echocardiographic findings.
An ECG and chest x-ray are obtained. ECG typically shows changes of LV hypertrophy with or without an ischemic ST- and T-wave pattern. Chest x-ray findings may include calcification of the aortic cusps (seen on the lateral projection or on fluoroscopy) and evidence of HF. Heart size may be normal or only mildly enlarged.
Prognosis
AS may progress slowly or quickly and thus requires regular follow-up to detect progression, particularly in sedentary elderly patients. In such patients, flow may become significantly compromised without triggering symptoms.
Overall, about 3 to 6% of asymptomatic patients with normal systolic function develop symptoms or LV ejection fraction depression every year. However, surgery is usually delayed until symptoms develop because the risk of surgery outweighs the survival benefit in asymptomatic patients. Surgery should not be delayed once symptoms develop. Mean survival in untreated symptomatic patients is about 2 to 3 yr. Aortic valve replacement relieves symptoms and improves survival. Risk with surgery increases for patients who require simultaneous coronary artery bypass graft (CABG) and for those with depressed systolic LV function.
About 50% of deaths occur suddenly. While awaiting surgery, patients with severe AS should be advised to restrict physical exertion.
Treatment
Asymptomatic patients with a maximum gradient ≤ 25 mm Hg and a valve area > 1.0 cm2 have a low mortality and low overall risk of requiring surgery in the next 2 yr; annual evaluation for symptom progression, including echocardiography to determine gradient and valve area, is appropriate.
Asymptomatic patients with gradients of 25 to 50 mm Hg or valve area < 1.0 cm2 are at higher risk of developing symptoms in the next 2 yr, but generally elective valve replacement is not required in the absence of symptoms. Valve replacement is indicated for patients who have moderate or severe AS and primarily require CABG. Surgery may be indicated for patients who become hypotensive during exercise treadmill testing and for those with LV ejection fraction < 50%. Patients with ventricular arrhythmias and severe LV hypertrophy are also often referred for surgery, but benefits are less clear. Recommendations for patients without any of these qualifying conditions include more frequent monitoring for progression of symptoms, LV hypertrophy, gradients, and valve area with medical management as needed. It is unclear whether statins reduce the progression of AS. Other drugs may be detrimental, especially those that can cause hypotension. Small studies suggest that perhexilene maleate may decrease symptoms. Nitroprusside has been used as a temporizing measure to reduce afterload in patients with decompensated HF in the hours before valve replacement, but because this drug can have the same effect as rapid-acting nitrates, it must be used cautiously and monitoring is required.
Symptomatic patients should undergo valve replacement or balloon valvotomy. Valve replacement is indicated for virtually all who can tolerate surgery. In younger patients, the patient's own pulmonic valve can be used, providing good durability; a bioprosthesis is then used to replace the pulmonic valve (Ross procedure). Most often, the aortic valve is replaced with a mechanical or bioprosthetic valve. Preoperative evaluation for CAD is indicated so that CABG and valve replacement, if indicated, can be done during the same procedure.
Balloon valvotomy is used primarily in children and very young adults with congenital AS. In older patients who are unfit for surgery, balloon valvuloplasty can provide temporary relief of symptoms, perhaps for 6 to 12 mo, and can be repeated in selected patients. Minimally invasive percutaneous valve replacement is being used as an alternative procedure in very elderly or frail patients.
Last full review/revision March 2007 by Paul H. Tanser, MD
Content last modified June 2010
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